The present invention relates to a light emitting display device for displaying a number or a letter by selectively lighting a plurality of light emitting portions provided on its display surface. It also relates to a method of making such a light emitting display device. Examples of such light emitting display device include a so-called eight segments light emitting display device including seven light emitting segments in the form of a bar arranged to form a number xe2x80x9c8xe2x80x9d, and one dot segment for displaying a decimal point. Further, there exists a so-called dot matrix light emitting display device in which a plurality of dot segments are arranged in a matrix.
An example of prior art light emitting display device is shown in FIG. 16. The light emitting display device includes a casing 3 having an obverse surface which is formed with eight light emitting portions 4 comprising seven bar segments and one dot segment. Each of the light emitting portions 4 comprises a light guide perforated through the casing 3 in the height direction of the casing and a light emitting element such as an LED arranged at the bottom of the light guide. The light emitting display device further includes a plurality of leads, and each of the LEDs is bonded at a first end of one lead and is wire-bonded to a first end of another lead. Each of the leads has a second end, and the second ends extend along opposite side surfaces of the casing 3 toward the reverse side of the casing 3. In this way, each of the LEDs is electrically connected to an anode lead and a cathode lead. At this time, one of the anode and the cathode of each LED can be common with another LED. Therefore, in the case of eight segments light emitting display device as shown in FIG. 16, at least nine leads are provided to project from the reverse side of the casing 3.
Such a light emitting display device is formed using a so-called leadframe which includes lead portions. The LEDs are chip-bonded and wire-bonded on such a leadframe. Then a casing 3 is disposed over the leadframe so that each of light guides positionally corresponds to respective one of the LEDs. Then, after a tape is applied on the obverse surface of the casing 3 for prevention of resin flow, light-permeable resin is injected into the casing 3 from its reverse side and hardened. As a result, the light guides are filled with the light-permeable resin, and the first ends of the leads at which the LED chips and the wires are bonded are sealed with the light-permeable resin. Then, unnecessary portions of the leadframe are removed and the tape is peeled off, thereby providing a light emitting display device as shown in FIG. 16.
To display plural figures for example, a plurality of light emitting display devices need to be laterally aligned on a board without any space therebetween. Therefore, no leads can be extended out to the sides of the casing 3. This is because the leads 1 are extended vertically straight from the reverse surface of the casing 3. Such a light emitting display device is mounted on a board which is formed with a plurality of holes in advance. Each of the leads 1 is inserted in a respective hole of the board, and is soldered at the reverse surface of the board. The casing 3 is formed with a leg 31 at each of its four corners. The legs 31 determine the height of the casing 3 relative to the board when the leads are inserted into the holes.
The light emitting display device having the structure described above has the following problems.
Specifically, mounting of such a light emitting display device on a board, which is performed by inserting leads 1 into the holes of the board, cannot be easily automated. Such a mounting method is complicated because it is difficult to position the plurality of leads relative to the holes of the board because the leads 1 hide behind the casing 3 and can not be seen from above. Further, if a lead 1 is bent even partially, insertion of the lead into a hole is impossible. Moreover, when each of the leads is appropriately cut in advance for adjusting its length, the cut-off piece may remain at the cutting end of the lead 1, which hinders insertion of the lead into the hole.
On the other hand, surface mounting using reflow soldering is known as an easier and more efficient method of mounting an electronic component on a board. A surface mounting type light emitting display device is disclosed in JP-A-11-135839, for example. In the disclosed device, a necessary number of LEDs are mounted on an insulating substrate which is formed with a predetermined wiring pattern and terminals electrically connected to the wiring pattern. A casing formed with segments which direct light from the LEDs to the outside is mounted on the substrate. However, the manufacturing process of such a light emitting display device is more complicated than the light emitting display device of a leadframe type shown in FIG. 16, and hence requires a high manufacturing cost.
An object of the present invention is to provide a light emitting display device which can be manufactured from a leadframe and which may be mounted with other such light emitting display devices in close side-by-side relationship. The present invention also relates to a method of making such a light emitting display device.
In accordance with a first aspect of the present invention, there is provided a light emitting display device comprising a casing of a predetermined height having an obverse surface formed with a plurality of display segments each of which is provided at an end of a light guide, a plurality of light emitting elements disposed in the casing so as to positionally correspond to the display segments, a plurality of leads each of which has a first end electrically connected to a respective light emitting element and a second end extending toward a bottom side of the casing, and a resin filled in the light guides for sealing the first ends of the leads and the light emitting elements.
The second end of each lead is formed with a soldering surface which is provided in the casing to be substantially flush with a bottom surface of the casing in the height direction of the casing.
Preferably, the bottom side of the casing may have a peripheral portion formed with a plurality of legs.
Preferably, each of the soldering surfaces may be formed by bending, at the bottom side of the casing, the second end of a respective lead extending in the height direction of the casing at an acute angle.
Preferably, the second end of each lead may be bent toward a center of the casing.
Preferably, a spacer may be interposed between the resin and the second end of each lead.
Preferably, the second end of each lead may be formed with a flat portion which is substantially flush with the bottom surface of the casing in the height direction of the casing, and the second end is bent to define an obtuse angle at one end of the flat portion and/or at the other end of the flat portion.
Preferably, the plurality of leads are arranged in two rows extending along opposite sides of the casing, and the leads in one of the rows positionally deviates from the leads in the other row in the direction in which the rows extend.
In accordance with a second aspect of the present invention, there is provided a light emitting display device comprising: a casing having a predetermined height, the casing including an obverse surface, two longitudinally extending side walls and two widthwise extending side walls, the obverse surface being formed with a plurality of display segments each of which is provided at an end of a light guide; a plurality of light emitting elements disposed in the casing so as to positionally correspond to the display segments; a plurality of leads each of which has a first end electrically connected to a respective light emitting element and a second end extending toward a bottom side of the casing; and a resin filled in the light guides for sealing the first ends of the leads and the light emitting elements; the light emitting display device being used in combination with other light emitting display device or devices arranged in side-by-side relationship.
The plurality of leads are arranged in two rows extending along the two widthwise extending side walls, the second end of each lead being formed with a soldering surface.
Preferably, the soldering surface may be substantially flush with a bottom surface of the casing in the height direction of the casing.
Preferably, the casing may be rectangular or substantially rectangular in plan view.
Preferably, each of the longitudinally extending side walls may be formed with a leg.
Preferably, the soldering surface may be formed by bending the second end of each lead.
Preferably, the soldering surface may be located slightly lower than a bottom surface of the casing.
Preferably, the soldering surface may be formed by bending the second end of each lead inwardly. A spacer may be interposed between the resin and the second end of each lead.
Preferably, the leads may be bent so that portions of the leads extending outward from the resin are inclined alternately in opposite directions.
In accordance with a third aspect of the present invention, there is provided a method of making a light emitting display device comprising: a casing of a predetermined height having an obverse surface, two longitudinally extending side walls and two widthwise extending side walls, the obverse surface being formed with a plurality of display segments each of which is provided at an end of a light guide; a plurality of light emitting elements disposed in the casing so as to positionally correspond to the display segments; a plurality of leads each of which has a first end electrically connected to a respective light emitting element and a second end extending toward a bottom side of the casing; and a resin filled in the light guides for sealing the first ends of the leads and the light emitting elements.
The method comprises the steps of:
(a) bonding the light emitting elements on a leadframe including the leads and performing wire-bonding;
(b) disposing the casing on a leadframe so that the display segments positionally correspond to the light emitting elements;
(c) injecting a transparent resin into the casing for filling the light guides and solidifying the resin for sealing the first ends of the leads, the light emitting elements and bonding wires; and
(d) separating the leads from the leadframe and bending the second end of each lead for forming a soldering surface.
Preferably, in the step (d), the soldering surface is formed to be substantially flush with a bottom surface of the casing in the height direction of the casing.